Intracellular protein breakdown in non-growing cells of Escherichia coli

Abstract

When E. coli leu- was incubated at 35 degrees in a medium based on minimal medium, but with the omission of phosphate ions, or glucose, or NH4+ ions and leucine, intracellular protein was degraded at a rate of about 5 percent/hr. in each case. If Mg2+ ions were omitted, however, the rate of degradation was 2.9 percent/hr. Under certain conditions of incubation, protein degradation was inhibited. The inhibitor was neither NH4+ ions nor amino-acids, and its properties were not those of a protein, but it might be an unstable species of RNA. Although a large part of the cell protein was degraded at about 5 percent/hr. during starvation of NH4+ ions and leucine, some proteins were lost at more rapid rates, whereas others were lost at lower rates or not at all. In particular, [beta]-galactosidase activity was lost at about 8 percent/hr. during starvation of NH4+ ions and leucine, whereas D-serine-deaminase and alkaline-phosphatase activities were stable. During starvation of Mg2+ ions, all three enzyme activities were stable.